Surgical tether apparatus and methods of use

ABSTRACT

A spinal treatment system includes a constraint device having an upper tether portion, a lower tether portion and a compliance member coupled therebetween. The upper tether portion is coupled with a superior spinous process of a spinal segment in a patient and the lower tether portion is coupled with an inferior spinous process or sacrum of the spinal segment. The length or tension in the constraint device is adjustable so that the construct of the tether portions and the compliance member provides a force resistant to flexion of the spinal segment. The system also includes a first prosthesis coupled with the spinal segment, wherein the constraint device modulates loads borne by the prosthesis or by tissue adjacent thereto.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 12/721,198, filed on Mar. 10, 2010, now U.S. Pat. No.8,562,653, which is a non-provisional of, and claims the benefit of U.S.Provisional Patent Application No. 61/158,892 filed Mar. 10, 2009, theentire contents of which are incorporated herein by reference.

The present application is also related to U.S. Provisional PatentApplication No. 61/158,886, the entire contents of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to medical methods andapparatus. More particularly, the present invention relates to methodsand apparatus used to restrict flexion of a spinal segment. The methodsand apparatus disclosed herein may be used alone or in combination withother orthopedic procedures such as those intended to treat patientswith spinal disorders. Exemplary spinal disorders include but are notlimited to back pain as well as joint problems, vertebral fractures,intervertebral disc, nucleus and annulus problems.

A host of spinal conditions exist which often result in mobility issuesand/or back pain. A major source of chronic low back pain is discogenicpain, also known as internal disc disruption. Discogenic pain can bequite disabling, and for some patients, can dramatically affect theirability to work and otherwise enjoy their lives. Patients suffering fromdiscogenic pain tend to be young, otherwise healthy individuals whopresent with pain localized to the back. Discogenic pain usually occursat the discs located at the L4-L5 or L5-S1 junctions of the spine. Paintends to be exacerbated when patients put their lumbar spines intoflexion (i.e. by sitting or bending forward) and relieved when they puttheir lumbar spines into extension (i.e. by standing or archingbackwards). Flexion and extension are known to change the mechanicalloading pattern of a lumbar segment. When the segment is in extension,the axial loads borne by the segment are shared by the disc and facetjoints (approximately 30% of the load is borne by the facet joints). Inflexion, the segmental load is borne almost entirely by the disc.Furthermore, in flexion the nucleus shifts posteriorly, changing theloads on the posterior portion of the annulus (which is innervated),likely causing its fibers to be subject to tension and shear forces.Segmental flexion, then, increases both the loads borne by the disc andcauses them to be borne in a more painful way. It would therefore bedesirable to provide methods and apparatus that reduce or modulateloading on the disc and adjacent tissue.

A number of treatments exist for addressing back pain and spinalmobility. Some of these include the use of artificial discs, artificialnucleus replacement, annulus repair, kyphoplasty treatment of vertebralfractures, instrumentation of the spinal segment with or withoutconcomitant fusion, and facet joint replacement. Many of thesetreatments are promising, yet in some cases they also have potentialdrawbacks. For example, when spinal fusion is performed, excessivemotion or loading of spinal segments may result. Often, the excessivemotion or loading and consequent effects occur at a level adjacent thefusion (referred to as adjacent segment degeneration or junctionalsyndrome). This can result in further degeneration of the motionsegments. Therefore, it would be desirable if flexion at adjacentlevel(s) of the spinal segment were restricted, thereby reducing oreliminating the excessive motion and any further degeneration.

Other treatments such as disc replacement, nucleus replacement, annulusrepair, facet joint repair, and vertebral fracture repair could alsobenefit from restricted flexion in the vicinity of treatment area. Forexample, excessive flexion may loosen the purchase of a prosthesis tothe anatomical structures, such as by toggling the pedicle screws thatanchor a prosthetic facet joint device. Restricting flexion in thevicinity of the treatment area modulates loads borne by these implantsor by surrounding tissue thus reducing, eliminating, or mitigatingiatrogenic damage to tissue as well as reducing loads borne by anyprostheses and adjacent tissue and further providing additional flexionstability.

For the aforementioned reasons, it would therefore be advantageous toprovide methods and apparatus that modulate loads borne by implants usedin spinal surgery. It would also be desirable if such methods andapparatus would also modulate loads borne by tissue in the vicinity ofthe surgically treated region and also provide additional flexionstability. It would further be desirable if the apparatus and methodsproviding the flexion stability preserved the natural motion andphysiology of the patient so as to allow the patient to maintainmobility and minimize or avoid detrimental clinical effects caused byforces resulting from non-physiological loading. It would be furtherdesirable if such methods and apparatus were minimally invasive to thepatient, cost effective, and easy to use. It would further be desirableif such methods and apparatus were resistant to damage or failure overrepetitive loading conditions in the body.

2. Description of the Background Art

Patents and published applications of interest include: U.S. Pat. Nos.3,648,691; 4,643,178; 4,743,260; 4,966,600; 5,011,494; 5,092,866;5,116,340; 5,180,393; 5,282,863; 5,395,374; 5,415,658; 5,415,661;5,449,361; 5,456,722; 5,462,542; 5,496,318; 5,540,698; 5,562,737;5,609,634; 5,628,756; 5,645,599; 5,725,582; 5,902,305; Re. 36,221;5,928,232; 5,935,133; 5,964,769; 5,989,256; 6,053,921; 6,248,106;6,312,431; 6,364,883; 6,378,289; 6,391,030; 6,468,309; 6,436,099;6,451,019; 6,582,433; 6,605,091; 6,626,944; 6,629,975; 6,652,527;6,652,585; 6,656,185; 6,669,729; 6,682,533; 6,689,140; 6,712,819;6,689,168; 6,695,852; 6,716,245; 6,761,720; 6,835,205; 7,029,475;7,163,558; Published U.S. Patent Application Nos. US 2002/0151978; US2004/0024458; US 2004/0106995; US 2004/0116927; US 2004/0117017; US2004/0127989; US 2004/0172132; US 2004/0243239; US 2005/0033435; US2005/0049708; 2005/0192581; 2005/0216017; US 2006/0069447; US2006/0136060; US 2006/0240533; US 2007/0213829; US 2007/0233096;2008/0009866; 2008/0108993; Published PCT Application Nos. WO 01/28442A1; WO 02/03882 A2; WO 02/051326 A1; WO 02/071960 A1; WO 03/045262 A1;WO2004/052246 A1; WO 2004/073532 A1; WO2008/051806; WO2008/051423;WO2008/051801; WO2008/051802; and Published Foreign Application Nos.EP0322334 A1; and FR 2 681 525 A1. The mechanical properties of flexibleconstraints applied to spinal segments are described in Papp et al.(1997) Spine 22:151-155; Dickman et al. (1997) Spine 22:596-604; andGarner et al. (2002) Eur. Spine J. S186-S191; Al Baz et al. (1995) Spine20, No. 11, 1241-1244; Heller, (1997) Arch. Orthopedic and TraumaSurgery, 117, No. 1-2:96-99; Leahy et al. (2000) Proc. Inst. Mech. Eng.Part H: J. Eng. Med. 214, No. 5: 489-495; Minns et al., (1997) Spine 22No. 16:1819-1825; Miyasaka et al. (2000) Spine 25, No. 6: 732-737;Shepherd et al. (2000) Spine 25, No. 3: 319-323; Shepherd (2001) MedicalEng. Phys. 23, No. 2: 135-141; and Voydeville et al (1992) OrthopTraumatol 2:259-264.

BRIEF SUMMARY OF THE INVENTION

The present invention generally relates to medical methods andapparatus. More particularly, the present invention relates to methodsand apparatus used to restrict flexion of a spinal segment. The methodsand apparatus disclosed herein may be used alone or in combination withother orthopedic procedures such as those intended to treat patientswith spinal disorders. Exemplary spinal disorders include but are notlimited to back pain as well as joint problems, vertebral fractures,intervertebral disc, annulus and nucleus problems.

In a first aspect of the present invention, a surgical method comprisesimplanting a first prosthesis into the patient where the firstprosthesis is engaged with at least a portion of a spinal segment in thepatient. The method also includes the step of implanting a constraintdevice into the patient, with the constraint device having an uppertether portion, a lower tether portion and a compliance member coupledtherebetween. An upper portion of the constraint device is engaged witha superior spinous process and a lower portion of the constraint deviceis engaged with an inferior spinous process or a sacrum. The length ortension in the constraint device is adjusted so that the construct ofthe tethers and compliance member provides a force resistant to flexionof the spinal segment. The length or tension may be adjusted to adesired value. Also the constraint device modulates loads borne by thefirst prosthesis or tissue adjacent thereto. The constraint device mayindirectly modulate these loads. The first prosthesis may comprise bonegraft.

In another aspect of the present invention, a spinal treatment systemcomprises a constraint device having an upper tether portion, a lowertether portion and a compliance member coupled therebetween. The uppertether portion is coupled with a superior spinous process of a spinalsegment in a patient and the lower tether portion is coupled with aninferior spinous process or sacrum of the spinal segment. Length ortension in the constraint device is adjustable so that the construct ofthe compliance member and tethers provides a force resistant to flexionof the spinal segment. The system also includes a first prosthesiscoupled with the spinal segment, wherein the constraint device modulatesloads borne by the prosthesis or by tissue adjacent thereto.

In yet another aspect of the present invention, a spinal treatmentsystem comprises a first prosthesis comprising a plurality of pediclescrews and at least one spinal stabilization rod. The first prosthesisis adapted to instrument a pair of vertebrae to be fused. The pair ofvertebrae is disposed in a spinal segment of a patient, and at least onepedicle screw is threadably engaged with at least one each of thevertebrae to be fused. The stabilization rod is coupled with the atleast one pedicle screw and also the stabilization rod is disposedacross the pair of vertebrae to be fused. A constraint device comprisesa compliance member, with the constraint device being superior to atleast a portion of the pair of vertebrae to be fused. A lower portion ofthe constraint device is operatively coupled with at least one of thepedicle screws, and the constraint device length or tension isadjustable to so as to provide a force resistant to flexion of thespinal segment superior to the vertebrae to be fused. Alternatively, alower portion of the constraint device may be operatively coupleddirectly with one of the fused vertebra, such as by encircling thespinous process of the fused vertebra. The constraint device length ortension may be adjusted to a desired value. The constraint device alsomodulates loads borne by the first prosthesis and tissue adjacentthereto. The constraint device may comprise an upper tether portion thatis disposed at least partially around a superior spinous process or anupper portion of the compliance member may be operatively coupled with apedicle screw that is threadably engaged with a pedicle superior to theinstrumented region of the spinal segment. In alternative embodiments,the embodiment described above may be inverted so that the constraintdevice may be inferior to at least a portion of the pair of vertebrae tobe fused.

Sometimes the first prosthesis may comprise an artificial disc that isimplanted between adjacent vertebrae. The disc may be implanted from aposterior, anterior, lateral, or other approach and the adjacent tissuemay comprise an intervertebral disc, vertebral body, endplate or facetjoints which may be adjacent the artificial disc. In some embodiments,the first prosthesis may comprise an artificial facet joint.

Sometimes, at least one of the first prosthesis or the constraint devicemay comprise a therapeutic agent that is adapted to modify tissue in thespinal segment. The therapeutic agent may comprise a bone morphogeneticprotein or one of its precursors, or another agent whose effect is tomodify the load-bearing characteristics of the spinal segment.

The method may further comprise the steps of fusing two adjacentvertebrae together with bone grafting material and implanting the firstprosthesis may comprise coupling a substantially inelastic tether to thesuperior vertebra of the two vertebrae that are fused or will be fusedtogether, wherein the construct of the substantially inelastic tetherand lower tether portion limits flexion between the two vertebra thatare fused or that will be fused together. The construct of theconstraint device also provides a force that is resistant to flexion ofthe supradjacent or the subjacent motion segment or pair of vertebrae.The substantially inelastic tether also may be disposed between theupper and lower tether portions. The substantially inelastic tether maybe disposed at least partially around a superior surface of anintermediate spinous process. The inelastic tether may also be disposedthrough a notch or hole in intermediate spinous process. Additionaldisclosure on notching or creating an aperture in a spinous process isdisclosed in U.S. Provisional Patent Application No. 61/149,224 filedFeb. 2, 2009, and International PCT Application No. PCT/US2010/022767,the entire contents of which are incorporated herein by reference. Theintermediate spinous process may be disposed between the superiorspinous process and the inferior spinous process or the sacrum.

Sometimes implanting the first prosthesis comprises positioning a spacerbetween a pair of adjacent spinous processes. The pair of adjacentspinous processes between which the spacer is implanted may be disposedsuperior to at least one of the superior spinous process, the inferiorspinous process, or the sacrum, and the spacer may inhibit extension ofat least a portion of the spinal segment at which it is implanted. Theforce provided by the construct of the compliance member and tethers mayresist flexion of a portion of the spinal segment inferior to thespacer. In other embodiments, implanting the first prosthesis maycomprise positioning a spacer between a pair of adjacent spinousprocesses that are disposed inferior to at least one of the superiorspinous process, or the inferior spinous process. The spacer inhibitsextension of at least a portion of the spinal segment at which it isimplanted and the force provided by the construct of the compliancemember and tethers may resist flexion of a spinal segment that issuperior to the spacer.

Implanting the first prosthesis may comprise inserting a prostheticnucleus into a disc disposed between adjacent vertebrae. Duringsegmental flexion, wedging of the vertebral endplates may force theprosthetic nucleus dorsally. Adjusting length or tension in theconstraint device may inhibit migration or expulsion of the prostheticnucleus away from the center of the disc. The tension of the constraintdevice may be modified or re-adjusted either transcutaneously or in asecond surgical procedure. This allows the constraint device toinitially be adjusted to a higher tension during an initial period oftime after nucleus implantation when greater segmental stiffness isdesirable. The higher initial stiffness facilitates soft tissue healingand also minimizes the risk of early nucleus migration from the disc.After the initial healing period, tension may be re-adjusted to adesired value, such as to a lower value in order to decrease segmentalstiffness. The method may further comprise fully removing a disc orpartially removing disc material between adjacent vertebrae of thespinal segment. The constraint device may modulate loading on the discspace, a prosthetic nucleus placed, or region and any remaining discmaterial. The constraint device may inhibit re-herniation of the discafter discectomy. The first prosthesis may comprise an annular repairdevice that is configured to repair or compensate for an injury ordefect in an annulus fibrosus of the spinal segment. Implanting thefirst prosthesis may comprise implanting the annular repair device froma posterior approach. The constraint device may inhibit migration orexpulsion of the annular repair device from the annulus fibrosus.

Implanting the first prosthesis may comprise injecting a filler materialsuch as bone cement into a vertebra. Implanting the first prosthesis maycomprise treating a fractured vertebra with kyphoplasty orvertebroplasty. The constraint device may modulate loading on thevertebra.

The step of implanting the constraint device may comprise piercing aninterspinous ligament to form a penetration superior to superior surfaceof the superior spinous process and advancing the upper tether portionthrough the penetration. The step of implanting the constraint devicemay also comprise piercing an interspinous ligament to form apenetration inferior to an inferior surface of the inferior spinousprocess and advancing the lower tether portion through the penetration.In other embodiments, the constraint device may be advanced through anotch or aperture in either of the superior or inferior spinousprocesses, as disclosed in U.S. Provisional Patent Application No.61/149,224, and International PCT Application No. PCT/US2010/022767previously incorporated herein by reference. Alternatively, theconstraint device may be advanced through a gap between the superiorspinous process and an adjacent spinous process, or a gap between theinferior spinous process and an adjacent spinous process. The gap may becreated by surgical removal of an interspinous ligament therefrom duringa decompression or other procedure. Adjusting length or tension in theconstraint device may comprise adjusting the length or tension aplurality of times during treatment of the spinal segment and during orafter healing of the spinal segment. Adjusting length or tension mayfurther comprise transcutaneous adjustment after the initialimplantation procedure is completed. Sometimes, the region extendingdirectly between an inferior surface of the superior spinous process anda superior surface of the inferior spinous process may remain free ofprostheses.

In some embodiments, the method may further comprise fusing a pair ofadjacent vertebrae of a spinal segment in a patient. Fusing the pair ofadjacent vertebrae may further comprise instrumenting the pair ofadjacent vertebrae with a plurality of pedicle screws and at least onestabilization rod disposed therebetween. The method may also compriseimplanting a constraint device into the patient, the constraint deviceengaging a vertebra adjacent to the fused pair of vertebrae, typicallyimmediately superior to but potentially immediately inferior to thefused pair of vertebrae. The constraint device may comprise a compliancemember with a portion of the constraint device operatively coupled witha pedicle screw system or coupled directly to one of the fusedvertebrae. The method also may include the step of adjusting length ortension in the constraint device, thereby providing a force resistant toflexion of the spinal segment and modulating loads borne by theinstrumented adjacent vertebrae and tissue adjacent thereto. The lengthor tension may be adjusted to a desired a value.

The constraint device may comprise an upper tether portion that isdisposed at least partially around or through a superior spinousprocess. Alternatively, an upper portion of the compliance member may beoperatively coupled with a fastener that is coupled with a pediclesuperior to the instrumented region of the spinal segment. The fastenermay comprise a pedicle screw. In alternative embodiments, the constraintdevice may also be attached to the inferior adjacent segment. Thus, theconstraint device may comprise a lower tether portion that is disposedat least partially around or through an inferior spinous process orsacrum. Alternatively, the lower portion of the compliance member may beoperatively coupled with a fastener such as a pedicle screw, that iscoupled with a pedicle inferior to the instrumented region of the spinalsegment or directly coupled to the spinal segment, inferior of the fusedvertebrae.

These and other embodiments are described in further detail in thefollowing description related to the appended drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram illustrating the lumbar region of thespine.

FIG. 1B a schematic illustration showing a portion of the lumbar regionof the spine taken along a sagittal plane.

FIG. 2 illustrates a spinal implant of the type described in U.S. PatentPublication No. 2005/0216017A1.

FIGS. 3A-3B illustrate the use of a constraint device with an artificialdisc and/or an artificial facet joint.

FIGS. 4A-4C illustrate the use of a constraint device supradjacent to aspinal fusion.

FIG. 5 illustrates the use of a constraint device with an interspinousspacer.

FIGS. 6A-6B illustrate the use of a constraint device with an artificialnucleus.

FIGS. 7A-7D illustrate the use of a constraint device in addition tokyphoplasty.

FIGS. 8A-8B illustrate the use of a constraint device with an annularrepair device.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A is a schematic diagram illustrating the lumbar region of thespine including the spinous processes (SP), facet joints (FJ), lamina(L), transverse processes (TP), and sacrum (S).

FIG. 1B is a schematic illustration showing a portion of the lumbarregion of the spine taken along a sagittal plane and is useful fordefining the terms “neutral position,” “flexion,” and “extension” thatare often used in this disclosure.

As used herein, “neutral position” refers to the position in which thepatient's spine rests in a relaxed standing position. The “neutralposition” will vary from patient to patient. Usually, such a neutralposition will be characterized by a slight curvature or lordosis of thelumbar spine where the spine has a slight anterior convexity and slightposterior concavity. In some cases, the presence of the constraint ofthe present invention may modify the neutral position, e.g. the devicemay apply an initial force which defines a “new” neutral position havingsome extension of the untreated spine. As such, the use of the term“neutral position” is to be taken in context of the presence or absenceof the device. As used herein, “neutral position of the spinal segment”refers to the position of a spinal segment when the spine is in theneutral position.

Furthermore, as used herein, “flexion” refers to the motion betweenadjacent vertebrae of a spinal segment as the patient bends forward.Referring to FIG. 1B, as a patient bends forward from the neutralposition of the spine, i.e. to the right relative to a curved axis A,the distance between individual vertebrae L on the anterior sidedecreases so that the anterior portion of the intervertebral disks D arecompressed. In contrast, the individual spinous processes SP on theposterior side move apart in the direction indicated by arrow B. Flexionthus refers to the relative movement between adjacent vertebrae as thepatient bends forward from the neutral position illustrated in FIG. 1B.

Additionally, as used herein, “extension” refers to the motion of theindividual vertebrae L as the patient bends backward and the spineextends from the neutral position illustrated in FIG. 1B. As the patientbends backward, the anterior ends of the individual vertebrae will moveapart. The individual spinous processes SP on adjacent vertebrae willmove closer together in a direction opposite to that indicated by arrowB.

Back pain may be caused by a number of conditions associated with thespinal segment, and many different types of spinal interventions andprostheses have been developed to address such conditions. Examples oftreatments administered in an effort to alleviate back pain and relatedproblems include replacement or modification of a disc or disc nucleus,repair of an annulus fibrosus, repair of vertebral fractures withkyphoplasty or vertebroplasty, facet joint replacement, and spinalfusion. These treatments are promising but in some circumstances mayhave drawbacks. For example, spinal prostheses or surgical proceduresmay adversely modify loading in the spinal column, causing excessive orotherwise detrimental loads to be borne by the prostheses or by treatedor adjacent tissue. Such loads may result in loosening, migration orexpulsion of a prosthesis, a significant risk for a prosthetic disc,facet, nucleus, or annular repair device, and a risk also fortraditional fusion hardware. In addition, such loads may injure atreated site while it is still healing and vulnerable to mechanicaldamage and result in iatrogenically damaged tissue; this is particularlytrue for kyphoplasty. Over time, such loads may lead to degeneration oftissue adjoining a treatment site, as has been observed for segmentsadjacent to a spinal fusion. Furthermore, such loads may result inincreased wear and tear on prostheses, decreasing such prostheses'useful lifetimes and potentially leading to device failures. Forexample, in the case of artificial discs, the disc edges often impingeon one another thereby causing cracking, wear, tissue inflammation aswell as other device failure modes. Often, these detrimental loads aregreatest or significantly exacerbated in segmental flexion. Flexion isthe largest component of the intervertebral range of motion and is themost frequently exercised; as described previously, flexion increasesloading on the intervertebral disc space and is associated with commonspinal pathologies. It would therefore be desirable to provide methodsand apparatus that can be used alone or in conjunction with other spinaltreatments to help reduce the excessive loading and to provideadditional flexion stability.

Spinal stabilization is typically accomplished with instrumentation suchas pedicle screws and stabilization rods. Placement of such traditionalinstrumentation in many cases requires major surgery with significantoperative morbidities and a long healing period, can be painful, maylimit patient mobility, and can result in undesirable wear and tear onthe instrumentation itself as well as on adjacent bone and other tissue.Rather than relying on direct stabilization and direct load bearinginstrumentation, the present approach disclosed herein utilizes indirectunloading and indirect stabilization of the affected spinal segment byconstraining flexion, preferentially biasing the motion of the spinalsegment into extension where it is inherently more stable. The spinalsegment is biased into this position using an adjustable constraintdevice that provides a variable force resistant to flexion. Using anindirect approach to augment stability of the spine provides a uniqueway to improve the mechanical loading environment for implanted spinaldevices, surgically treated tissue, and adjacent tissue.

Another major advantage of using the present devices and methods is thatno loading other than tensile loading is transferred to the constraintdevice, and thus the constraint device is likely to experience fewerfailure modes than traditional instrumentation in which significant,complex loading is transferred to the screws and rods. The presentconstraint device therefore, not only attempts to maximize therapeuticeffectiveness, but also attempts to minimize failure, while mostexisting spinal instrumentation maximizes load-bearing andconsequentially has a high rate of mechanical failure.

There are other advantages of the present methods and apparatus. Forexample, traditional instrumentation with pedicle screws andstabilization rods crowds the surgical field and can limit a surgeon'saccess to a targeted region. In addition, such instrumentation limitsthe space available for implantation of other devices, especiallydevices that must be coupled to the spinal segment with screws. Thepresent stabilization methods preferably avoid the use of screws,although screws may be used, allowing implantation of other screw-baseddevices if necessary. Additionally, less tissue resection is required toimplant the present devices and methods relative to traditionalinstrumentation, providing a less invasive procedure with multiplecorresponding clinical and economic benefits including less blood loss,shorter procedure time, faster healing, and a lower treatment cost.

Additionally, when traditional instrumentation such as pedicle screwsand rods is used, the spinal segment, once instrumented, is locked intoa given position. Even with dynamic stabilization rods, only limitedmotion is permitted. A rod-and-screw approach thus relies on the skillof the surgeon to determine the optimal position of the spinal segmentprior to instrumenting it. The present devices and methods areadvantageous because they do not “lock” the spinal segment into a rigidposition. The present devices and methods are adjustable in situ andallow some movement of the spinal segment after implantation, reducingthe need to establish a single optimal position before the implantationoccurs. If this adjustability contributes to more consistent fit betweenthe device and surrounding tissues, healing around the device and insurrounding tissue may occur in a more natural manner. The presentdevices may also be adjusted in later procedures after initialimplantation and are thus likely to be better at accommodating changesover time compared to rigid instrumentation systems.

Another major challenge associated with traditional instrumentation suchas rods and screws is the possibility of the devices failing due toshearing, bending, rotation, loosening, etc. The present device is notrigid and can accommodate these types of motions and therefore is lesslikely to fail in service. Because of its potentially lower failurerate, the present device should generate fewer safety concerns and alower complication rate.

The present devices and methods also preserve more natural motion of thespinal segment and have unique kinematic signatures compared with otherrigid or “flexible” instrumentation devices. Unlike pedicle screw androd instrumentation, the present devices and methods tend to encourageengagement of the facets. This results in some indirect restriction ofaxial rotation, which may provide additional spinal segment stability.The present device disclosed herein intentionally allows backward motion(extension) which helps avoid issues with extension loading and may helpwith balancing of the patient's vertebral column. Most otherinstrumentation devices or systems do not permit backward motion of thespinal segment.

Based on the challenges associated with many existing back paintreatments and stabilization methods, it would therefore be desirable toprovide methods and apparatus that can be used alone or in conjunctionwith other spinal treatments to help reduce the excessive loading and toprovide additional flexion stability. FIG. 2 shows a spinal implant ofthe type described in related U.S. Patent Publication No. 2005/02161017A1, now U.S. Pat. No. 7,458,981 the entire contents of which areincorporated herein by reference. The constraint device of FIG. 2 may beused alone or in combination with other spinal treatments to modulateloads borne by prostheses implanted into the patient or borne by tissueadjacent the treatment area and to thereby facilitate healing and reducewear and tear. Furthermore, the constraint device may be used to providegreater stability to the spinal segment.

Many of the prostheses and procedures which can benefit from theconstraint described herein were designed to be self-sufficient, suchthat a specific pathology is directly treated by the intervention.Examples include the treatment of a defect in the annulus fibrosis withan annular repair device and the treatment of a vertebral compressionfracture with a kyphoplasty or vertebroplasty. While these interventionsdirectly address the pathology, they often do not address secondary ortransitory effects that they precipitate, as described above; as such, afurther need for improvement over many stand-alone interventions exists.It should be noted that the adjunctive stabilization may be implantedconcurrently with the primary prosthesis or procedure; or may beimplanted at a later date to address degenerative changes associatedwith the detrimental loading of the primary prosthesis or adjacenttissue.

A limited number of implants are known that combine motion-preservationapproaches to address multiple pathologies simultaneously; for example,the PDS by Disc Motion Technologies, is a combination of facetreplacement device and total disc replacement prosthesis. However, suchcombination devices are intended to address two independent primarypathologies occurring in combination—for example, the combined discreplacement and facet replacement device addresses combined pathology ofthe facet joint and the disc. It would be advantageous to provide ameans with which improve the results of a primary treatment byaugmenting and modulating the biomechanics of the primary treatment. Itwould further be advantageous for the adjunctive therapy or constraintto be minimally invasive, to avoid the use of pedicle screws due to theknown associated complications and morbidities, and to allow forphysiologic loading and motion in concert with the intention of theprimary motion-preservation treatment.

As illustrated in FIG. 2, an implant 10 typically comprises a tetherstructure having an upper strap component 12 and a lower strap component14 joined by a pair of compliance members 16. The upper strap 12 isshown disposed over the top of the spinous process SP4 of L4 while thelower strap 14 is shown extending over the bottom of the spinous processSP5 of L5. The compliance member 16 will typically include an internalelement, such as a spring or rubber block, which is attached to thestraps 12 and 14 in such a way that the straps may be “elastically” or“compliantly” pulled apart as the spinous processes SP4 and SP5 moveapart during flexion. In this way, the implant provides an elastictension on the spinous processes which is a force that resists flexion.The force increases as the processes move further apart. Usually, thestraps themselves will be essentially non-compliant so that the degreeof elasticity or compliance may be controlled and provided solely by thecompliance members 16. The implant 10 may be coupled to the spinalsegment in a minimally invasive manner. Typically, a small puncture iscreated in the interspinous ligament (not illustrated) superior to thesuperior spinous process and also inferior to the inferior spinousprocess. The upper and lower straps may then be advanced through thesepiercings and the ends coupled together to form a closed loop.Additional details on implant 10 and the methods of use are disclosed inU.S. Provisional Patent Application Nos. 61/093,922; 61/059,543;61/059,538; U.S. patent application Ser. No. 12/106,103; U.S. PatentPublication Nos. 2010/0023060; and 2008/0262549; U.S. Pat. No.7,458,981; and International PCT Application Nos. PCT/US2009/055914; andPCT/US2009/046492; the entire contents of each is incorporated in itsentirety herein by reference. A number of exemplary embodiments in whicha constraint device is used in combination with other spinal treatmentsare disclosed below. The constraint devices disclosed herein may includeany of the features described in the references incorporated byreference. Features from various embodiments of constraint devices mayalso be combined or substituted with features from other embodimentsdisclosed herein.

FIGS. 3A-3B illustrate the use of a constraint device with an artificialdisc or artificial facet joint replacement device. In FIG. 3A, a naturalintervertebral disc D is normally disposed between two adjacentvertebrae V. However, due to disease or degeneration, the damaged discmay be replaced with an artificial disc 302. Artificial discs are wellknown in the art and exemplary commercial devices include the Charitéartificial disc from Depuy Spine, a Johnson & Johnson Company, as wellas other devices from Synthes and Medtronic Sofamor Danek. Theartificial disc 302 replaces the natural disc D and restores properalignment and spacing between the two vertebrae V and allows smoothrelative motion between the two vertebrae V.

FIG. 3B illustrates the implantation of an artificial replacement facetjoint 306 which may be used alone or in combination with the artificialdisc implant. Facet joint replacements are also well known in the artsuch as the Acadia provided by Facet Solutions, Inc. In some patients,facet joints are repaired or replaced with a joint prosthesis in orderto eliminate the pathological, painful joint; restore normal motion andprovide stabilization of the spinal segment. Also, facet joint implantsmay be used as an adjunct to partial laminectomy, laminotomy, neuraldecompression and facetectomy, in lieu of fusion. Facet joint implantsare often used to treat instabilities or deformities of the lumbar spineincluding degenerative disease of the facets, degenerative disease ofthe facets with instability, degenerative spondylolisthesis and spinalstenosis.

Neither artificial discs nor facet joint replacement devices typicallyprovide an elastic resistance to flexion of the spinal segment. Theseprostheses have bearing surfaces that are designed to minimize frictionand may comprise a “hard stop” that limits travel. Therefore, applying aconstraint device 304 around adjacent spinous processes SP helps limitflexion in the spinal segment. Constraint device 304 generally takes thesame form as the constraint device illustrated in FIG. 2 and includes anupper tether portion, a lower tether portion and a pair of compliancemembers (only one illustrated in the lateral view of FIG. 3). The uppertether portion is disposed around a superior surface of a superiorspinous process and the lower tether portion is disposed around aninferior surface of an inferior spinous process. The method for applyingthe constraint device is disclosed in greater detail in U.S. PatentPublication No. 2008/0262549 and additional disclosure on the constraintdevice may be found in U.S. patent application Ser. No. 12/106,103 andU.S. Pat. No. 7,458,981; all previously incorporated herein byreference. The methods for implanting the constraint device may beapplied to any of the embodiments disclosed herein and any of theconstraint devices disclosed herein may take the form of constraintdevice 304. Moreover, by limiting flexion, some of the loading appliedto the artificial disc or artificial facet joint and adjacent tissue ismodulated. For the disc, this change in loading may minimize disc edgeimpingement, reducing the need for more complex artificial discs withfeatures that limit edge impingement. The loading is more evenlydistributed or even lessened. Thus, applying a constraint device helpsrestore more natural biomechanics in the spinal segment.

FIGS. 4A-4C illustrate how the constraint device of FIG. 2 may be usedin conjunction with fusion of a spinal segment. In FIG. 4A adjacentvertebrae are fused together using methods well known in the art. Thefused region F is often instrumented with pedicle screws 402 and spinalstabilization rods 404 to prevent motion at the level of the fusion,although in situ fusions may be performed without internal fixation.While this procedure is promising, it may also have potential drawbacks.For example, after spinal fusion is attained, excessive motion mayresult at adjacent levels (e.g. spinal segment regions above and belowthe fused region F). This is due to compensation for loss of flexibilityat the fused segment and can result in further degeneration of themotion segments. Therefore, it would be desirable if flexion of segmentsat adjacent levels (e.g. above or below the fusion) were restrictedthereby reducing or eliminating any further degeneration. In FIG. 4A, aconstraint device 406 such as the one illustrated in FIG. 2 is appliedto the motion segment superior to the fused region. The constraintdevice is secured to the spinal segment such that it is completelyindependent of the fusion instrumentation. Here, the constraint deviceis disposed around the superior surface of a superior spinous processsuperior to the fusion and also around an inferior surface of aninferior spinous process, the inferior spinous process being a part ofsuperior region of the fused spinal segment. Thus, in this embodiment,motion along the instrumented region is substantially inhibited in orderto facilitate the fusion process and the constraint device restrictsflexion of the spinal segment supradjacent to the fused region. Thishelps more evenly distribute and possibly lessen loading applied to thefusion instrumentation as well as adjacent tissue, particularly theadjacent intervertebral disc. It also reduces excessive motion andlessens the chance of further degeneration of the non-fused motionsegments.

FIG. 4B illustrates an embodiment similar to that of FIG. 4A with themajor difference being that in FIG. 4B, the constraint device is coupledwith the fusion instrumentation. In FIG. 4B, the lower vertebra is fusedwith another vertebra (not illustrated). The fused region F is theninstrumented with pedicle screws 402 and spinal stabilization rods 404to prevent motion between the fused vertebrae. A constraint device 408is then applied supradjacent to the fused segment. In this embodiment,the constraint device 408 includes an upper tether 410 disposed around asuperior surface of a superior spinous process and a pair of compliancemembers 412 which provide the force resistant to flexion of the spinalsegment. Here, the bottom of each compliance member 412 is anchored withthe pedicle screw 402 and stabilization rod 404. Thus, the constraintdevice 408 limits flexion of the spinal segment supradjacent to thefused region F. In alternative embodiments, the upper portion of thecompliance member 412 may include a coupling bar 416 illustrated inphantom that is coupled with a pedicle screw or other fastener 414instead of using the upper tether 410. In alternative embodiments, theconstraint could be turned around such that the constraint device isinferior to the fused region and a top portion of the compliance membersare coupled with a pedicle screw.

FIG. 4C illustrates lateral and posterior views of an alternativeembodiment of a constraint device similar to that of FIG. 2 that may bemodified to provide resistance to flexion as well as prevent motion of afused spinal segment. In FIG. 4C, a posterolateral fusion F is performedbetween adjacent vertebrae, here L4 and L5. A constraint device 420includes an upper tether portion 422 and a lower tether portion 426. Theconstraint device 420 is coupled with the spinal segment such that theupper tether portion 422 is disposed around the superior surface of asuperior spinous process of a vertebrae adjacent the fused region andthe lower tether portion 426 is disposed around an inferior surface ofan inferior spinous process on the inferior portion of the fused region.An intermediate tether 424 is disposed around the superior surface of anintermediate spinous process and the ends of the intermediate tether 424are secured to the lower tether portion 424. The intermediate spinousprocess is disposed between the superior and inferior spinous processesto which the constraint device is coupled, and in this exemplaryembodiment, the intermediate spinous process is a part of the upperfused vertebra. In this embodiment, the upper, lower and intermediatetether portions 422, 424, 426 are substantially inelastic, thus motionbetween the inferior spinous process and the intermediate spinousprocess is controlled based on the tension or length in the tetherportions 424, 426. It would therefore be desirable to adjust theintermediate tether portion and the lower tether portion such that nomotion or very limited motion is permitted in the fused segment.Additionally, the construct of the upper tether portion 422, the lowertether portion 426 and compliance member 408 restrains flexion of thesupradjacent segment. One of skill in the art will appreciate that inalternative embodiments, the constraint device could also be used suchthat flexion of the spinal segment inferior to the fused region isrestricted.

In many of the embodiments disclosed herein, no implant is placed inbetween the constraint device. Thus, when a constraint device is coupledwith a superior surface of a superior spinous process and an inferiorsurface of an inferior spinous process, the region extending directlybetween an inferior surface of the superior spinous process and asuperior surface of the inferior spinous process often remains free ofany spacers or other implants.

Unlike previous embodiments in which nothing is placed between spinousprocesses, in FIG. 5 an interspinous spacer is used in combination witha constraint device to limit extension and flexion of spinal segments.In FIG. 5, a spacer 502 such as the X Stop provided by St. FrancisMedical Technologies, Inc. (acquired by Kyphon, Inc., now a part ofMedtronic) is positioned between spinous processes SP on L3 and L4. Thespacer limits extension between adjacent vertebra thereby potentiallyreducing facet loading and increasing the area of the spinal canal andforamen. This helps relieve patients' systems such as neurogenicclaudication and pain. A constraint device 504 may also be applied tothe spinal segment in order to limit flexion. In FIG. 5, constraintdevice 504 includes an upper tether portion 506, compliance members 508and a lower tether portion 510. The upper tether portion in thisembodiment is shown directly coupled with the spacer 502. It may beattached to the spacer with a number of methods including bonding,welding, fixturing, passing it through an aperture, etc. In alternativeembodiments the upper tether portion need not be coupled with thespacer. Instead, the tether may be disposed around a superior surface ofa superior spinous process similar to the embodiments of FIGS. 2, 3, and4A-4C previously discussed. The lower tether portion 510 is disposedaround an inferior surface of an inferior spinous process. Thus, flexionis limited in the segment inferior to the spacer and the construct ofthe tethers and compliance members 508 provide a force resistant toflexion. One of skill in the art will appreciate that the spacer may bedisposed between any two spinous processes along the spinal segment,thus constraint device position may be moved along the spinal segment asrequired.

An artificial or prosthetic nucleus may be used instead of a total discprosthesis when disc degeneration is at an early or intermediate stageand the disc annulus is still competent and provides adequateconstraint. By replacing only the nucleus, remaining disc tissues suchas the annulus and endplates are preserved along with their functions.The surgical procedure for replacing the nucleus may be simpler than atotal disc replacement. In FIG. 6A, an artificial nucleus 602 isimplanted into the remaining disc annulus A that is disposed betweenvertebrae V. The prosthetic nucleus 602 re-inflates the annulus andrelieves compressive loads by carrying a portion of the load. However,the nucleus 602 may experience undesired migration, expulsion, wear orother negative effects due to segmental flexion. FIG. 6A illustratespartial extrusion of nucleus 602. A constraint device similar to that ofFIG. 2 which restricts flexion may help prevent extrusion of thenucleus. In FIG. 6B, constraint device 604 is applied to the upper andlower spinous processes of the vertebrae surrounding the artificialnucleus 602. The constraint device 604 generally takes the same form asthe constraint devices previously described. For example, constraintdevice 604 includes an upper tether portion 606, a lower tether portion610 and a pair of compliance members 608 (only one shown in the lateralview of FIG. 6B). The upper tether portion 606 is disposed around asuperior surface of a superior spinous process and the lower tetherportion 610 is disposed around an inferior surface of an inferiorspinous process. Constraint device 604 resists flexion of the spinalsegment surrounding the artificial nucleus, thus distributing forcesmore evenly on the artificial nucleus and surrounding tissue, therebypreventing damage to and expulsion of the nucleus.

FIGS. 7A-7D illustrate the use of a constraint device in conjunctionwith kyphoplasty. In patients having a spinal fracture, also referred toas a vertebral compression fracture, often the result of osteoporosis,cancer or benign tumor, kyphoplasty may be an appropriate minimallyinvasive treatment. FIG. 7A illustrates a spinal fracture 702 in avertebra V. FIG. 7B illustrates the main steps in a kyphoplastyprocedure. In kyphoplasty, a hollow instrument is used to create anarrow pathway into the fractured bone 702. An orthopedic balloon 704 isthen inserted through the pathway into the fractured vertebral body 702.Often, two balloons are used, one on each side of the vertebral body, toprovide better support to the bone during the treatment (FIG. 7B is alateral view and therefore only illustrates one balloon). The balloons704 are then inflated in order to raise the collapsed vertebral body andreturn it to its normal position. Inflating the balloons also creates acavity in the bone and once the balloons are deflated, the cavity isfilled with bone cement 706 or a bone cement analogue, thereby formingan internal cast that holds the vertebral body in position. Again, thisis a promising treatment, but flexion bending motions as indicated bythe arrow in FIG. 7C may exert higher compressive loads on the anteriorportion of the repaired vertebra. These loads may be transferred to therepaired fracture 708 potentially causing pain, non-union of thefractured bone and other healing failures. In addition, the stiffness ofthe repaired vertebral body may be greater than that of the nativevertebral body because the elastic modulus of bone cement and most bonecement substitutes is greater than that of the normal bone; as such,there could be excessive wear and tear at the bone cement-boneinterface. Application of a constraint device that limits flexion mayhelp offload the repaired fracture and adjacent tissues 708 therebyreducing these adverse complications. In FIG. 7D a constraint devicesimilar to that of FIG. 2 is applied to the spinal segment treated withkyphoplasty. The constraint device 710 generally takes the same form aspreviously described above. The constraint device 710 includes an upperand lower tether portion 712, 716 that are disposed around the spinousprocesses adjacent the spinal fracture. In this embodiment, the uppertether portion 712 is disposed around a superior surface of a superiorspinous process and the lower tether portion 716 is disposed around aninferior portion of an inferior spinous process of the fracturedvertebra. The construct of the tethers and a pair of compliance members714 (only one illustrated in the lateral view of FIG. 7D) provide theforce resistant to flexion of the treated spinal segment. Otherembodiments may include variations on kyphoplasty including but notlimited to vertebroplasty (injection of a filler material withoutexpansion of the kyphoplasty balloon) and implants (e.g. implantation ofstent-like or mesh-like devices).

FIGS. 8A-8B illustrate the use of a constraint device with an annularrepair device. Annular repair devices are used to patch or repair adefect, lesion, tear or other injury in the annulus fibrosus, especiallyone due to a disc herniation. FIG. 8A illustrates an annular defect 804in an intervertebral disc between adjacent vertebrae V. An annularrepair device 802 is coupled with the annulus in order to prevent discherniation or nucleus expulsion. Herniations are often acutelyassociated with flexion, indicated in FIG. 8A by the arrows, which mayalso inhibit healing and induce re-herniation. Similarly, flexionmotions may place more demands on annular repair devices, thus impactingtheir effectiveness. A constraint device that restricts flexion motionsmay help reduce the incidence of re-herniation and improve outcomes forpatients treated with an annular repair device, in particular aminimally invasive device.

FIG. 8B illustrates the use of a constraint device such as the one seenin FIG. 2 in conjunction with the annular repair device 802. Theconstraint device generally takes the same form as those previouslydescribed above. Constraint device 806 includes upper and lower tetherportions 808, 812 and a pair of compliance members 810 (only one seen inthe lateral view of FIG. 8B). The upper tether portion is disposedaround a superior surface of a superior spinous process and the lowertether portion is disposed around an inferior surface of an inferiorspinous process. The construct of the tethers and compliance members 810provide a force that limits flexion of the spinal segment. This alsohelps to reduce tension in the posterior annulus and keeps the annulardefect 804 closed.

In any of the embodiments disclosed above, tension and or length of theconstraint device may be adjusted in order to control how muchresistance to flexion is provided. The constraint devices may beadjusted before, during or after implantation including transcutaneouslyso that additional surgery is avoided. This also allows the device to beadjusted as healing occurs. For example, a tighter constraint devicethat provides greater resistance to flexion may be provided during theinitial phase of healing and a less tight constraint device thatprovides less resistance to flexion may be required as healingprogresses. Various adjustment and locking mechanisms are disclosed inU.S. Provisional Patent Application Nos. 61/059,543; and 61/059,538;previously incorporated herein by reference, as well as other patentapplications incorporated herein. Furthermore, any of the embodimentsdisclosed herein may also be used to carry and deliver a therapeuticagent that facilitates the healing process. For example, antibiotics maybe carried by the constraint device to help prevent infection and bonemorphogenetic proteins may also used in order to help stimulate bone orother tissue growth. Additionally, many of the embodiments disclosedherein show the constraint device limiting flexion of a spinal segmentat the level of or superior to the level of the implant or treatment.One of skill in the art will appreciate that the constraint device maybe applied to the spinal segment so as to limit flexion below the levelof the implant or treatment. In addition, in some situations a lowerportion of the constraint device may be coupled with the sacrum insteadof an inferior spinous process. Sacral attachment methods are disclosedin greater detail in U.S. Provisional Patent Application No. 61/149,224;International PCT Application No. PCTfUS2010/022767; and U.S. patentapplication Ser. No. 11/827,980, the entire contents of which areincorporated herein by reference. In the embodiments described above,the constraint structure may be implanted concurrently with the firstprosthesis or procedure, or in a separate procedure performed at anothertime.

While the exemplary embodiments have been described in some detail forclarity of understanding and by way of example, a number ofmodifications, changes, and adaptations may be implemented and/or willbe obvious to those as skilled in the art. Hence, the scope of thepresent invention is limited solely by the independent claims.

What is claimed is:
 1. A surgical method for fusing a spinal segment in a patient, the spinal segment having a superior vertebra and an inferior vertebra, said method comprising: performing a fusion procedure on at least a portion of the spinal segment; implanting a constraint device into the patient, the constraint device having an upper tether portion, a lower tether portion and a compliance member coupled therebetween, wherein one of the upper or lower tether portions is coupled to a spinous process of a third vertebra or coupled to a sacrum, the third vertebra or the sacrum being adjacent the spinal segment, wherein the other of the upper or lower tether portion is coupled to a spinous process of the spinal segment, wherein the constraint device provides a force resistant to flexion of the spinal segment; and adjusting a length or tension of the constraint device so that the constraint device provides an elastic force resistant to flexion of the spinal segment.
 2. The surgical method of claim 1, wherein the constraint device modulates loads borne by the spinal segment or tissue adjacent thereto.
 3. The surgical method of claim 1, wherein performing the fusion procedure comprises instrumenting the spinal segment with pedicle screws and spinal stabilization rods.
 4. The surgical method of claim 1, wherein performing the fusion procedure comprises an in situ fusion.
 5. The surgical method of claim 1, wherein the third vertebra is superior to the spinal segment, and wherein the upper tether portion is disposed about a superior surface of the spinous process of the third vertebra.
 6. The surgical method of claim 5, wherein the step of implanting the constraint device comprises: piercing an interspinous ligament to form a penetration superior to the superior surface of the third spinous process; and advancing the upper tether portion through the penetration.
 7. The surgical method of claim 5, wherein the step of implanting the constraint device comprises: advancing the upper tether portion through a gap between a superior process of the spinal segment and the spinous process of the third vertebra, the gap created by surgical removal of an interspinous ligament therefrom.
 8. The surgical method of claim 1, wherein the third vertebra is inferior to the spinal segment, and wherein the lower tether portion is disposed about an inferior surface of the spinous process of the third vertebra.
 9. The surgical method of claim 8, wherein the step of implanting the constraint device comprises: piercing an interspinous ligament to form a penetration inferior to the inferior surface of the third spinous process; and advancing the lower tether portion through the penetration.
 10. The surgical method of claim 8, wherein the step of implanting the constraint device comprises: advancing the lower tether portion through a gap between a spinous process of the spinal segment and the spinous process of the third vertebra, the gap created by surgical removal of an interspinous ligament therefrom. 